A problem in connection with centrifugal separators of this kind is to bring the liquid supplied through the inlet tube to rotate with the rotor without a dispersed phase of the liquid being splitted by the shearing forces acting on the same, which makes the following separation of this phase out of the liquid more difficult. An efficient and gentle acceleration of the liquid is thus desired for obtainment of a maximum separation result in the centrifugal separator. A kind of acceleration and entrainment member often used is wings, which extend axially and radially and are supported by the rotor in the inlet chamber. However, these wings give rise to heavy strains on the supplied liquid in the form of shocks and shearing forces. If the inlet chamber is not filled during the operation all the way to the centre, these wings cause, in addition, splashing of the incoming liquid, which means that air is mixed with the liquid.
A proposed solution of the described problem is shown in the U.S. Pat. No. 2,302,381. The centrifugal separator shown therein has a rotor, which inside itself forms a separation chamber and an inlet chamber, the latter communicating with the separation chamber. The liquid mixture of components, which are to be separated, is supplied to the inlet chamber centrally through an inlet channel in the vertical driving shaft of the rotor. Inside the inlet chamber there is arranged a stack of annular discs, which are rotatable with the rotor. The centre of the discs coincides with the rotational axis of the rotor. Centrally every disc has a circular opening, which openings together form a reception chamber for the supplied liquid mixture. Between themselves the discs form passages through which the liquid mixture is intended to flow radially outwards towards the separation chamber.
In the centrifugal separator known from U.S. Pat. No. 2,302,381 the inlet channel ends below the said reception chamber. The inlet channel has an opening directed axially towards the reception chamber, the flow through the opening being strongly restricted. Upon supply of liquid mixture through the inlet channel, hereby, a jet is created, which passes through the reception chamber and hits a deflection member. This deflection member rotates with the rotor and deflects the liquid mixture in the jet radially outwards towards the annular discs, between which the liquid mixture flows further on towards the separation chamber.
In the passages between the discs the supplied liquid is brought to rotate with the rotor without being exposed to as heavy strains as entraining members in the form of wings give rise to in the same circumstances. On the contrary, both the strong restriction of the flow at the opening of the inlet channel and the collision between the created jet and the conical deflection member result in a strong turbulence and splitting of the components of the liquid mixture, which in many cases makes it impossible to achieve a satisfactory separation result.
In U.S. Pat. No. 4,721,505 there is shown an inlet device in a centrifugal separator, in which the supplied liquid mixture is intended to be accelerated in passages between discs of the same kind as the discs according to U.S. Pat. No. 2,302,381. In this inlet device the liquid mixture is supplied through a supply member to a central reception chamber, which is formed by central openings in the annular discs. An evacuating channel is connected to one of the axial ends of the reception chamber. Between the opening of the supply member in the reception chamber and the connection thereto of the evacuating channel a number of the discs are located. At the opening of the supply member a liquid body is maintained during operation, which extends through at least some of the passages between the discs. The supply member is so designed that the liquid mixture supplied through the same forms a liquid phase, which is continuous with the liquid body.
In the inlet device according to U.S. Pat. No. 4,721,505 the supply member extends axially through the central openings of a number of the discs. This limits the possible extension of the discs radially inwards, which in turn limits the entraining capability of the discs. In order to compensate for this and achieve the same maximum capacity the number of discs has to be increased, which means that the axial extension of the disc stack increases correspondingly. Besides, if the supply member is stationary it is necessary that there is a gap between this and the discs rotating with the rotor, which is big enough to prevent that the discs collide with the supply member when the rotor will oscillate. This means that the supply member has to be assembled with a very high degree of accuracy if the gap is not relatively big, which limits the radial extension of the discs further.